The present invention generally relates to the field of data communications. More specifically, embodiments of the present invention pertain to methods and systems for quality of service marking of data packets.
Quality of Service (QoS) for packet switched data communication networks provides preferential treatment to specific traffic in a network to ensure high-quality network performance. Without QoS, the network devices offer best-effort service to each packet. As a result, in some situations, packets are transmitted without any assurance of reliability, delay bounds, or throughput. Implementing QoS in a network makes performance more predictable and bandwidth utilization more effective. Thus, QoS methods ensure the required level of service without expanding or over-provisioning the network.
Typically, a packet is assigned a service-level (also called class-of-service) at the network edge. The method to indicate the service-level, throughout the network, depends on the packet's encapsulation standard. For example, for Ethernet packets, a 3-bit User Priority field, included in the Ethernet header, is used to indicate the service-level, providing up to 8 classes of service. For an IPvX packet, a 6-bit Differentiated Services Code Point (DSCP) field, included in the IP header, is used, providing up to 64 classes of service. In a MPLS network, a 3-bit EXP field, or the 20-bit label, in the MPLS header, are used to indicate the classes of service. These and other standards utilize various fields to propagate QoS information throughout the network, as will be evident to one of skill in the art.
The act of setting the service-level by a network device is called “QoS marking.” The marking operation defines the packet internal and external QoS handling. Internal QoS handling defines the set of actions, performed on the packet by the network device, to provide the required service-level and to assure that the System Level Agreement (SLA) is met. External QoS handling defines which QoS related fields in the packet header are modified by the network device in order to propagate the assigned service level throughout the network.
In some conventional switches, the packet's external marking is mapped at ingress to an internal DSCP value. In these conventional switches, IP traffic is generally mapped from the external DSCP value to the internal DSCP field without reclassification. For Ethernet traffic, the 3-bit User Priority field is mapped to the internal DSCP field using an 8-level to 64-level class of service map. Various maps or tables are used to generate the internal DSCP values for other types of traffic. The internal DSCP value is used as a single parameter that assigns the internal as well as the external QoS handling. In these conventional switches, the number of service levels is limited to 64 classes and the network administrator cannot control which QoS fields in the packet header are used to propagate QoS information. Some applications require more than 64 service levels or a stringent control over packet header modification. Thus, there is a need in the art for improved methods and techniques of marking packets